The present invention relates to a communication control apparatus, a communication control method, and an intermediate communication control unit. More particularly, the invention relates to a communication control apparatus, a communication control method, and an intermediate communication control unit preferably for use with an optical transmission apparatus which constitutes an optical communication network such as SONET (Synchronous Optical Network).
FIG. 48 is a block diagram showing an example of a common optical communication system. In FIG. 48, numeral 101 denotes an optical transmission apparatus, numeral 102 denotes an optical multiplexer for combining a number of signals equivalent to DS1 (Digital Signal Level 1) into a signal equivalent to OC (Optical Carrier)-3 (about 155.52 Mbps) by multiplexing, numeral 103A denotes a digital exchange, numeral 103B denotes an analog exchange, and numeral 104 denotes a carrier serving area (CSA) within which subscribers' terminals receive a variety of services.
The optical transmission apparatus 101 is a subscriber-side unit, and it combines signals (data) ranging from an audio frequency range (about 64 kbps) to OC-3 into a signal by multiplexing and transmit the thus multiplexed data to a receiving side through a SONET interface, such as an OC-3 interface or an OC-12 interface having a transmission rate four times that of the OC-3 interface (i.e., a transmission rate of about 622 Mbps). The optical transmission apparatus 101 makes it possible to increase the capacity of the analog exchange 103A and the digital exchange 103B, to add an electronic cross connecting function to the optical communication system, to use an optical fiber as a subscriber line (FITL: Fiber in The Loop), and to cope with the digital exchange 103A.
Specifically, as shown in FIG. 48, the optical transmission apparatus 101 is constituted by integration of a DLC (Digital Loop Carrier) 101B for controlling an access point through which services are offered to subscribers and an optical multiplexing section 101A for transmitting data through the access point. The DLC 101B classifies signals according to the types of subscribers' apparatuses and sends the thus classified signals by means of the previously described electronic cross connecting function. As a result, a variety of services [e.g., narrow band services (local SW services, and special services), wide band services (DS1, STS1, DS3, etc), and FITL] can be offered to the carrier service area 104 as a complex set of services.
If the analog exchange 103B is connected to the optical transmission apparatus 101, the previously described optical communication system is usually constituted by use of an interface unit 105A or 105B, whichever is desired, according to the type of service to be offered to the carrier service area 104, as shown in, e.g., FIG. 49(a). If the digital exchange 103A is connected to the optical transmission apparatus 101, the optical transmission apparatus 101 and the digital exchange 103A are connected to each other without the previously described interface units 105A and 105B being interposed between them, as shown in, e.g., FIG. 49(b).
The optical transmission apparatus 101 can be connected to various tributary shelves (service shelves) 101C to 101E depending on the type and form of service to be offered, as shown in, e.g., FIGS. 50 and 51, so that it can handle with various forms of service to be offered to subscribers. In the case of depicted in FIG. 51, as a result of a common shelf (CMS: Common Shelf) 101C being connected to a narrow band shelf (NBS: Narrow Band Shelf) 101D and a narrow band optical fiber shelf (NFS: Narrow Band Fiber Service Shelf) 101E, low-speed (narrow-band) services (e.g. a variety of telephone services to each subscriber's telephone 106) are offered to subscribers. It is possible to directly offer high-speed (wide-band) services from the common shelf 101C by use of only the common shelf 101C. In this case, an OC-3, STS1, and D3 interface (which have different transmission rates) are selectively used.
In FIG. 51, reference numeral 107 denotes subscriber-side interface shelves of FITL (OAS1: Optical Access Shelf-1), which are used when narrow-band optical fiber shelves 101E are utilized. Reference numeral 101F denotes a power feed shelf (PFS: Power Feed Shelf) in the optical transmission apparatus 101 for feeding electrical power to each of the interface shelves 107. With the above circuit configuration, it is possible to optically transmit signals to the vicinity of the subscriber's telephones 106 located in remote areas (that is, from NFS 101E to the interfaces 107).
FIG. 52 is a block diagram showing an example of the detailed configuration of the above-described narrow-band shelf (NBS) 101D. As shown in FIG. 52, the narrow-band shelf 101D comprises a plurality of slave units (CH: channel units) 111, a communication control section (AT1N) 112, a multiplexing/dividing section (MD1N) 113, and a power feeding section (PW1N) 114.
Each of the channel units 111 accommodates a plurality of subscriber lines [or the analog exchanges 101A shown in FIG. 49(a)], and the communication control section 112 executes alarm processing and overall control operations in the narrow-band shelf 101D. The communication control section 112 usually comprises a CPU (a central processing unit). The multiplexing/dividing section 113 combines signals DS0 from the channel units 111 into a signal DS1 through multiplexing, or separates the signal DS1 into the signals DS0. As shown in FIG. 52, the multiplexing/dividing section 113 is provided with two units, namely, one unit for use as a primary system (P) and the other unit for use as a spare system (W). The power feeding section 114 feeds electrical power to each unit within the narrow-band shelf 101D.
With such a circuit configuration, the communication control section 112 executes automatic scanning processing, control processing, and monitoring processing for each of the channel units 111 in the above described narrow-band shelf 101D. As a result of the collection of data regarding whether each channel unit 111 is mounted (connected) and data regarding the operating state of each channel unit 111, required processing such as alarm processing is carried out.
With regard to the previously described automatic scanning processing, control processing, and monitoring processing, the following principal operations are carried out for each of the channel units 111:
(1) Automatic Scanning Processing
Collection of data regarding the mounted state of each channel unit 111
(2) Control Processing
Writing of preset information, such as a gain adjustment value, to channel unit 111
Test access control for line test PA1 Control for turning on an alarm LED PA1 Monitoring the state of test access for line test PA1 Monitoring the state of a line (Idle/Busy) PA1 Monitoring the on/off state of an LED
(3) Monitoring Processing
Monitoring preset information such as a gain adjustment value
Collection of unit management information (a physical inventory) such as the date of manufacture and the name of a unit
The above-described narrow-band shelves (NBS) 101D are generally categorized into two types, namely, a serial communication type in which processing such as an automatic scanning processing is performed using serial transmission, and a bus communication type in which the above-described processing is performed using bus transmission.
As shown in FIG. 53, in the case of the serial communication type (which utilizes serial transmission), a communication control unit 112 is provided with a CPU 112' and a sub-communication control unit (SCON) 115A for performing serial transmission. Further, each channel unit 111 is provided with a similar sub-communication control unit (SCON) 115B and a register 116. The communication control unit 112 is connected to the channel units 111 through a corresponding number of serial buses.
In the serial communication type narrow-band shelf (NBS) 101D, the CPU 112' sends data, which are necessary for the automatic scanning processing, the control processing, and the monitoring processing, to the sub-communication control apparatus 115B through the sub-communication control apparatus 115A. As a result, the respective sub-communication control apparatus 115A and 115B execute the above-described various kinds of processing, and necessary data are collected every time each kind of processing is completed (i.e., every time an interruption signal (IRQ) is received from the sub-communication control apparatus 115A).
In contrast, in the case of the bus communication type (which utilizes bus transmission), the communication control unit 112 is provided with the CPU 112' and a buffer 115C, as shown in FIG. 54. Each channel unit 111 is provided with a buffer 115D and the register 116. The communication control unit 112 is connected to each of the channel units 111 through a set of signal lines (e.g., address signal lines, a data bus, and an enable signal line). The number of the sets of signal lines corresponds to the number of the channel units 111.
In the bus communication type narrow-band shelf (NBS) 101D, results of the automatic scanning processing, the control processing, and the monitoring processing are sequentially latched into the buffer 115C through the register 116 and the buffer 115D. Therefore, it becomes possible for the CPU 112' to arbitrarily collect necessary data without using the previously described interruption signal.
In the case of the serial communication narrow-band shelf (NBS) 101D, the number of signal lines (serial buses) between the communication control unit 112 and the channel units 111 can be reduced. The communication control unit 112 and each channel unit 111 usually communicate with each other through transmission and reception of data, for example, in units of one byte. Hence, the CPU 112' receives an interruption signal every one byte, which makes a program for controlling the CPU 112' complicated. As a result, the load on the CPU 112' becomes considerably large.
In the case of the bus communication type narrow-band shelf, it is possible to reduce the load on the CPU 112'. However, the number of lines (signal lines) increases as the number of channel units 111 is increased. In light of the recent tendency toward high-density packaging of the narrow-band shelves 101D associated with the miniaturization of the channel units 111, the bus communication type narrow-band shelf is very disadvantageous.
The present invention has been conceived in view of the above-described drawbacks, and an object of the present invention is to provide a communication control apparatus, a communication control method, and an intermediate communication control unit which can reduce a load on a master communication control unit while minimizing the number of signal lines between the master communication control unit and a plurality of slave units.